The present invention, in some embodiments thereof, relates to inkjet printing techniques and, more particularly, but not exclusively, to improved processes and compositions for formaldehyde-free inkjet printing of high resolution color images on absorptive and non-absorptive substrates of all colors.
The ever growing market of printing complex designs and images on almost every type of surface, and especially on knitted, woven and non-woven textile surfaces, plasticized and laminated fabrics (soft signage) and the likes, creates demands for new and more versatile printing technologies and materials. One such demand is for ink compositions and technologies which will be suitable for printing long lasting, durable, abrasion resistant, water-, detergent- and chemical-fast color images on a variety of materials, which will not wear out rapidly upon use, handling, washing and exposure to the environment. The garment industry is possibly the most demanding in terms of printing high quality and durable prints of textile, adding some requirements from the product, such as pleasant hand-feel of the printed area, flexible (bendable without cracking), stretchable and aerated print area, as well as fulfilling the requirement of Oeko-Tex Standard 100 (an international testing and certification system for textiles, limiting the use of certain chemicals, which was developed in 1992).
One of the most advanced techniques for achieving high-end printing results on fabrics and other pliable and absorptive surfaces is using polymerizable inkjet compositions by inkjet printing machines. Polymerizable ink compositions typically comprise a colorant dispersed in a polymerizable dispersant, mostly acrylic and urethane. These polymerizable ink compositions are generally applied on the substrate and then undergo curing to form a film, constituting the printed design or image. The film should be durable and affixed firmly to the substrate if long-lasting product is desired. Good film affixation to the substrate is typically afforded during the polymerization reaction (initiation, setting and curing) by use of crosslinking agents.
IL Patent No. 162231 and WO 2005/115089 by the present assignee, which are hereby incorporated by reference as if fully set forth herein, teach processes and systems for printing high quality, high resolution, multi-color images on fibrous or porous materials or other ink absorbing materials, or on materials having high surface tension with the ink liquid, and especially over garments, effected by applying a wetting composition prior to applying an ink composition and formation of the images. Specifically, the process of printing an image on a surface is effected by contacting at least a part of the surface, preferably covering slightly more than the area which is intended for the image, with a wetting composition so as to wet that part of the surface. The wetting composition is capable of interfering with the engagement of a liquid ink composition with material, such that when applying the liquid ink composition on the wetted surface, the ink is kept from smearing and absorbing in the material, allowing to form a high-quality image on the wet part of the absorptive surface. According to some embodiments disclosed in IL Patent No. 162231 and WO 2005/115089, the wetting solution is applied in a way so as to soak the textile media therewith.
U.S. Pat. No. 7,134,749 by the present assignee, which is hereby incorporated by reference as if fully set forth herein, teaches a method and apparatus for color printing on a dark textile piece. According to the teachings of this patent, the method includes the steps of digitally applying a white opaque ink layer directly onto a dark textile piece, and digitally printing a colored image on the white ink layer. Specifically, the method for color printing on a dark textile piece is effected by digitally printing, by means of an inkjet printing head, an opaque white ink layer directly onto a dark textile piece; and digitally printing a colored image on the white ink layer. The digital printing of the white ink layer is performed such that the white ink layer substantially covers, without exceeding, the designed area of the colored image, and the area of the image that should be white, and further such that the white ink layer and the colored image are substantially coextensive.
IL Patent Application No. 162231 and WO 2005/15089, all by the present assignee and incorporated by reference as if fully set forth herein, teach a process for printing an image on a substrate, which is effected by wetting a surface onto which an image is to be printed with a wetting composition that interferes with the engagement of the liquid ink composition with the surface and thus temporarily modifies the surface mechanical, physical and/or chemical characteristics, and thus contributes to the immobilization of the jetted droplets of ink on the substrate by minimizing the available time for the solid-liquid interface interactions which leads, for example, to absorption by wicking, or free-flowing of ink on top of non-adsorptive substrates which leads, for example, to smearing and bleeding of the ink. This immobilization of the droplets, effected by the temporary augmentation of the surface tensions of the surface, affords an image by an inkjet printing process, which is well affixed on the substrate and durable while still being characterized by high-resolution, high-definition and vivid colors, with no excessive bleeding and diffusion of the ink into the substrate.
U.S. Patent Application Nos. 2007/0103528 and 2007/0104899 teach improved and integrated methodologies for printing high quality, high resolution, multi-color images on lightly and/or darkly colored fibrous or porous materials or other ink absorbing materials, by providing a mechanism for drop immobilization aimed at inhibiting the adsorption by fabric, the bleeding, smearing, paddling and feathering of the jetted ink droplets. These integrated processes are effected by digitally printing a layer of an opaque, lightly colored ink composition, followed by digitally printing the colored image thereon, and optionally further involve applying a wetting composition prior to and/or subsequent to printing of these layers. These documents further provide multi-component compositions and processes utilizing wetting compositions and/or two-part liquid ink compositions which can interact therebetween as property-adjusting and property-sensitive pairs, so as to effect a chemical and/or physical change in one or more of these parts, and thus obtain improved binding and color perception of the resulting images on surfaces, particularly in cases of absorptive substrates. The ink drop immobilization is effected by adding a property-adjusting agent to either the liquid ink compositions or to a wetting composition and adding a property-sensitive agent, which promotes the gelation of the emulsion and precipitation and subsequent immobilization of the colorant to the substrate upon contacting the property-adjusting agent, to any of the wetting or liquid ink compositions which does not have the property-adjusting, while the curing finish results in crosslinking and affixing the polymer and colorants in the ink to the material of the substrate on its surface. Thus, the ink composition presented in these publications is made up of at least two parts which combine in situ on the surface of the substrate: a colorless part that is applied in order to interact with the colored part of the ink, thereby achieving at least a temporary immobilization of the colored part and minimize its absorption onto the substrate prior to printing the image, and another part containing the colorant which is applied in order to afford the image.
U.S. Patent Application having Publication No. 2011/0032319, which is incorporated by reference as fully set forth herein, teach a process of flattening and smoothing a textile substrate in preparation for inkjet printing and a device to effect the process. The disclosed process comprises spraying a fabric-based substrate with, for example, simple tap water, and then scraping the wet surface with a squeegee or pressing it with a roller, thereby forming a temporary flat surface in terms of protruding fibers or weaving dimples which affords improved conditions for printing highly sharp images thereon.
U.S. Patent Application having Publication No. 2011/0032304, which is incorporated by reference as fully set forth herein, teach multi-part inkjet ink compositions and processes for inkjet printing a high resolution and vivid color images on absorptive and stretchable substrates, such as spandex Lycra™ garments of all colors. This document teaches the use of proto-elastomeric, low Tg polymerizable agents in the composition, that congeal on the substrate before the polymerization reaction commences, thereby preventing feathering and bleeding of the colors into the fabric, and then cure to a firmly affixed stretchable film.
As mentioned above, the ingredient of the inkjet ink composition which can promote the formation of a polymeric/co-polymeric film, as well as promote bonding and affixation of the film to the substrate, is the crosslinking agent. The growing awareness among consumers, workers and manufacturers, has pushed the consumer-products market in general and the polymer industries in particular to search for compositions and processes which minimize or altogether nullify the use of harmful ingredients and the production of harmful by-products. One such by-product is formaldehyde, which is a by-product emitted during the polymerization and curing process of polymers using conventional crosslinking agents, such as amino resins. Albeit these crosslinking agents are highly effective, they contain at least 0.1-2.5% formaldehyde, and further emit more formaldehyde during the crosslinking reaction.
These days, any textile ink containing formaldehyde is restricted for use in certain applications, based on formaldehyde content of the garment according to Oko-Tex Standard 100 (Oeko-Tex). Although formaldehyde, which forms upon use of amino resin crosslinking agents, may evaporate from the garment at high temperatures, the levels of formaldehyde can never reach the allowed values according to the widely accepted Oko-Tex Standard 100 and Oko-Tex Standard 1000. Presently many manufacturers in the garment and consumer product industries prefer to refrain from using ink compositions containing or emitting formaldehyde to protect their employees and customers from exposure to formaldehyde.
U.S. Patent Application Nos. 2007/0218222, 2009/0122127 and 2010/0075045 and U.S. Pat. No. 7,748,838 disclose the use of glyoxal, a dialdehyde, as a crosslinking agent in ink compositions; U.S. Patent Application No. 2008/0241436 discloses the use of carbodiimides as crosslinking agents in ink compositions; U.S. Pat. Nos. 5,596,047, 6,063,922 and 7,381,347 teach carbamate functional 1,3,5-triazines and other crosslinking agents; and U.S. Pat. No. 7,723,400 and Kessel, N. et al. [J. Coat. Technol. Res., 5 (3) 285-297, 2008] teach the use of diacetone acrylamide in the context of an inkjet ink composition.
Additional prior art documents include U.S. Pat. Nos. 7,425,062, 7,381,347, 7,119,160, 6,124,398, 6,063,922, 5,596,047, 5,360,933, 4,888,093, 4,345,063, 4,285,690, 4,284,758, 3,100,704, and EP 0277361A1.